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transcript
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Neutron User’s Club
25 September 2001
NMS Ionising
Radiation Metrology
Programme 2001-04
Theme 3 Neutron
Metrology
David Thomas CIRM
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Theme 3 – Neutron Metrology
3.6 Van de Graaff /SAMES? MMF
FluenceStandards
3.1 Radionuclide-based 3.2 Accelerator-based
3.3 Comparisons & demonstration of equivalence
3.4 Neutron Spectrometry 3.5 Neutron Dosimetry Applications
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Project 3.1 – Radionuclide-based standards
Deliverables:
• Maintenance of manganese bath and
moderator detector
• Routine measurements of NPL source
emission rates
• Investigation of 250Cf in 252Cf sources
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250Cf in 252Cf
0 1 2 3 4 5 6 7 8 9 10
0
2
4
6
8
10
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Cfhlife.opj
Percentage error, as a function of age of the source and
% 250
Cf contamination if the half life is assumed to be that for 252
Cf
0% 250
Cf at age zero
5% 250
Cf at age zero
10% 250
Cf at age zero
15% 250
Cf at age zero
20% 250
Cf at age zero
% e
rror
for
'pre
dic
ted' em
issio
n r
ate
Age of source in half lives
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Project 3.2 – Accelerator-based standards
Deliverables
• Regular validation of fluence and energy standards
• Implement spectrometry for target condition
monitoring
• Time-of-flight developments
• Determination of long counter effective centres
• Determine optimum position for shadow cones
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Use of NPL fluence standards
• Routine calibrations/checks of area survey
instruments and personal dosemeters
• Type testing, mainly response function
measurements for old and new dosimetry
devices and spectrometers
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Types of measurements performed
Typical customers
• Secondary calibration labs, device manufacturers,
MoD, dosimetry services, Government
establishments
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Neutron area survey instruments
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Neutron personal dosemeters
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Project 3.3 – Comparisons for equivalence
Deliverables
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• Conclusion of thermal and
monoenergetic comparisons
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Project 3.5 – Neutron dosimetry
Deliverables
• 241Am-Be source international
comparison
• EUROMET survey instrument calibration
comparison
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• Conclusion of thermal and
monoenergetic comparisons
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Project 3.4 – Neutron Spectrometry
• Why should we do work on neutron spectrometry at NPL?
• To support the standards both radionuclide source based and accelerator based.
• To provide insight into the true extent of the problem of measuring neutron dose equivalent.
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10-3
10-2
10-1
100
101
102
103
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105
106
107
10-2
10-1
100
101
Thermal
Illustration of under- and over-read for some area survey instruments
areasurv.opj
Harwell 0949
EG&G LB6411
5" TEPC
H*(
10)
response
Neutron energy (MeV)
Neutron area survey meter responses
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Personal dosemeter responses
10-3
10-2
10-1
100
101
102
103
104
105
106
107
10-2
10-1
100
101
Thermal
Under- and over-read for samples of personal dosemeters
persdms.opj
Track-etch plastic P1
Track etch plastic P2
Track etch plastic P3
NTA film N1
Hp(1
0)
(10,0
o)
response
Neutron energy (eV)
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Measured neutron spectra
10-3
10-2
10-1
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101
102
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104
105
106
107
0.00
0.05
0.10
0.15
0.20
0.25
A selection spectra measured at sites in the nuclear industry
PWR fuel flask (France)
Fuel pin assembly area
Gas cooled reactor
Flu
ence
(E
* Φ
(E))
[cm
-2]
Neutron energy [eV]
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Project 3.4 – Neutron Spectrometry
Deliverables
• Maintenance and regular checks of spectrometers
• Use of battery powered electronics for Bonner sphere spectrometers
• Investigate combined unfolding of multiple spectrometers
• Improvements to response matrices
• Update SPKTBIB database
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Users of NPL Neutron Spectrometry service
• Power stations
• Cyclotron manufacturer
• Hospitals – around therapy LinAcs
• Fuel processing/reprocessing
• Radionuclide source manufacturers
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Project 3.5 – Neutron dosimetry
Deliverables
• Validate simple technique for neutron
measurements at LinAcs
• Characterise dual instrument system
• Measurements in realistic fields facility
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Realistic field spectrum
10-3
10-2
10-1
100
101
102
103
104
105
106
107
0.00
0.02
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Trawsfynydd
Calder Hall
NPL Realistic field
Gcreactcomp.opj
Gas-cooled reactors
E.Φ
(E)
Energy (eV)
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Real fields and calibration fields
10-3
10-2
10-1
100
101
102
103
104
105
106
107
0.00
0.05
0.10
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0.20
0.25
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Trawsfynydd
241
Am-Be
Cadarache realistic field
Gcreactcomp.opj
E.Φ
(E)
Energy (eV)
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Project 3.5 – Neutron dosimetry
Deliverables
• Extension of capabilities for dosimetry
with TEPCs
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• Characterise dual instrument system
• Validate simple technique for neutron
measurements at LinAcs
• Measurements in realistic fields facility
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Project 3.6 – Major facilities maintenance
Deliverables
• Maintenance of the Van de Graaff facility
• Development of the Van de Graaff facility
• Transfer of 14 MeV standard to AWE
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End